如何在安卓源码包中添加Retrofit、butterknife等外部库？

dependencies {
    // Retrofit
    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.9.0'

    // ButterKnife
    implementation 'com.jakewharton:butterknife:10.3.0'
    annotationProcessor 'com.jakewharton:butterknife-compiler:10.3.0'
}

android {
    // ...
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

android {
    // ...
    defaultConfig {
        // ...
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = [ 'butterknife.enabled': 'true' ]
            }
        }
    }
}